1. Field of the Invention
The present invention relates to a curvilinear motion guide unit, which is comprised of a track rail extending lengthwise curved with a preselected curvature, and a slider arranged for a curvilinear motion along the track rail by virtue of rolling elements.
2. Description of the Prior Art
Recently various types of bearing guide unit have been used incorporated between components movable relatively of each other in modern advanced machine tools, conveyors, industrial robots, transfer machines, assembling apparatus, semiconductor fabricating apparatus, and so on.
Disclosed in Japanese Patent Laid-Open No. 101914/1987 is bearing means for revolving motion, which comprises a guide rail curved to have a preselected radius of curvature and provided on both radially opposing sides thereof with raceway grooves for load areas through which balls are allowed to run, a slider having two confronting legs that are made on inwardly faced surfaces thereof with raceway grooves for load areas conforming in curvature with the raceway grooves on the guide rail, and turnaround means for non-loaded areas where the balls are allowed to recirculate through there. The prior bearing means has a detachable cover, which can be opened to take the balls in and/or out of the slider. The cover when closed keeps the balls against falling away from the slider. Moreover, the turnaround means for non-loaded areas is provided by a tubular member of J-pattern, which is divided into halves opposing to one another.
Another Japanese Patent Laid-Open No. 186028/1988 discloses a curvilinear sliding-motion bearing system equivalent in construction with the bearing means for revolving motion cited just above, in which a slider containing rolling elements therein can move along a circular guide rail. The known curvilinear sliding-motion bearing system is designed for sliding components in devices and systems as diverse as machine tools, industrial robots, any conveying systems or the like to guide or transfer commodities or parts along any curvilinear line from a home or reference station to any other demand positions. The curvilinear sliding-motion bearing system is comprised of a movable platform provided therein with both raceway grooves for load areas and other raceway grooves for non-loaded areas, which are connected one another through turnarounds in end covers attached to the platform, to form endless raceways allowing rolling elements to recirculate through them, and a track rail made with raceway grooves confronting the raceway grooves in the platform to provide the load areas of the recirculation passages for the ball. The track rail is formed in arc or circle, and the confronting raceway grooves for the load areas in the platform and on the track rail are made so as to describe imaginary circles having centers of curvature, which are common to each other and also in alignment with the center of curvature of an imaginary circle along the track rail. Thus, the rolling elements or balls can run through the load areas defined between the confronting raceway grooves, while continuing to carry loads in all directions. With the curvilinear sliding-motion bearing system stated earlier, the adjustment of pre-loading can be performed by selecting balls somewhat larger in size than the clearance between the confronting raceway grooves for the load areas, or varying the clearance between the confronting raceway grooves by tightening bolts.
Moreover, a recirculating-curvilinear motion bearing system for revolving motion has been known in, for example, Japanese Patent Publication No. 11213/1987, in which bearing blocks movable along a circular track rail are arranged at angular intervals around the circular track rail. The circular track rail is made on only radially outside surface thereof with two rows of raceway grooves while the bearing block is also made on only its inside with two rows of raceway grooves confronting the raceway grooves on the track rail to form between them load areas through which balls run to carry the load. The bearing block has return passages of non-loaded areas for recirculating the balls. The balls in the load areas come in rolling contact with the associated raceway grooves at two radially opposing sectorial portions thereof. With the bearing system for revolving motion described just above, the bearing blocks can revolve around the radially outside of the circular track rail by virtue of balls. An eccentric bolt is arranged between the bearing block and a turntable mounted on the bearing block to urge the bearing block towards the circular track rail, adjusting finely the pre-loading.
Another type of curvilinear motion rolling guide unit has been developed, as unveiled in for example Japanese Patent Laid-Open No. 30638/1998, in which a slider is installed for sliding movement on a curved spline shaft extending lengthwise with a desired curvature. In the prior curvilinear motion rolling guide unit, the slider has a casing that is slashed off diagonally at lengthwise opposing ends thereof, which thus come perpendicular to the centroidal axis of the spline shaft. While the casing is more subjected at its radially outside half to the load than at its radially inside half, the outside half is longer lengthwise than the inside half because the opposing ends are tilted whereby the load may be made balanced between the inside and outside halves. Similar curvilinear motion guide units to that stated earlier are further disclosed in Japanese Patent Laid-Open Nos. 21441/1996 and 21440/1996.
In addition, a recirculating-ball linear motion bearing system has been known as in, for example, Japanese Patent Publication No. 2809/1992, which is comprised of an elongated track rail of rectangular shape in cross section having on its widthwise opposing upright surfaces raceway grooves, each to each upright surface, and a slider casing made with raceway grooves confronting the raceway grooves on the track rail, and rolling elements arranged in load areas defined between the confronting raceway grooves to allow the slider casing to move linearly. For recirculation of the rolling elements, return passages for non-loaded areas are made in the slider casing at locations above any upper shoulders of the track rail and closer to the centroidal axis than the shoulders of the track rail.
To this day, yet a variety of curvilinear motion guide units for moving the slider along the curved guide way have been conventionally proposed as stated earlier, and no commercially viable curvilinear motion guide unit has been developed. In the curvilinear motion guide unit where the track rail extends curved with a preselected curvature, the application of the slider similar in construction to the slider currently available for the prior linear-motion rolling guide units becomes problematic because the raceway grooves on the slider needs extending curved in compliance to the track rail and, therefore, the slider is required to afford to provide the return passages in the widthwise inward/outward areas. This causes a corresponding increase in widthwise dimension of the casing for the slider, thus, resulting in the major problem of failing in making the slider slim or compact with well balance. With the prior curvilinear motion guide units, moreover, it is required to always stock a variety of end caps different in specification depending on the diverse specifications of the curvature of the track rail and the overall length of the slider. This eventually raises disadvantages of increasing the number of parts required and rendering the management of parts and components much complicated.
The present invention, therefore, has as its primary object to overcome the major problem in the prior curvilinear motion guide units in which a slider can move along a track rail extending curved with a preselected curvature. More particular, it relates to a curvilinear motion guide unit in which the slider has a casing modified in location where return passages are arranged and in configuration of lengthwise opposing ends, thereby reducing an overall widthwise dimension of the slider to make the casing compact or slim in size. The improved curvilinear motion guide unit of the present invention makes it possible to adopt virtually identical end caps just as they are, even if the curved track rail varies in curvature and/or overall length, thereby making each part for the specific end cap interchangeable. Accordingly, the slider movable along the curved track rail may be made compact or slim with well balancing and further the control of parts and components can be simplified to be economical.
The present invention is concerned with a curvilinear motion guide unit comprising a track rail extending curved with a preselected curvature and having lengthwise sides made thereon with first raceway grooves, and a slider fitting astride over the track rail for movement in a sliding manner along the track rail; wherein the slider is comprised of a casing provided with second raceway grooves extending curved in conformity with the first raceway grooves and return passages formed corresponding to the second raceway grooves, end caps mounted on forward and aft end faces of the casing, each to each end face, and provided therein with turnarounds connecting the second raceway grooves to the return passages, rolling elements running through recirculating passages composed of curved raceways defined between the first and second raceway grooves, the turnarounds and the return passages, and end seals attached on the end caps, each to each cap; and wherein the forward and aft end faces of the casing are each arranged such that an imaginary plane including any one of the end faces and normal to a top surface of the track rail coincides with a radial plane extending through the center of curvature of the track rail, and the return passages are opened on the forward and aft end faces at locations that are closer to a centroidal axis of the track rail than locations where the raceways are made open on the forward and aft end faces.
With the curvilinear motion guide unit constructed as stated earlier, where the return passages in the casing are made open on the end caps and the raceways are made open on the end caps always remain in preselected locations irrespective of the variations in curvature of the track rail. Moreover, the turnarounds are also made in the end caps at locations that are predetermined in conformity with the locations on the end caps where the return passages and raceways are made opened.
In accordance with one aspect of the present invention, a curvilinear motion guide unit is disclosed, wherein the lengthwise sides of the track rail are radially outside and inside curved surfaces having a common center of curvature coinciding with the center of curvature of the track rail.
In accordance with another aspect of the present invention, a curvilinear motion guide unit is disclosed, wherein the slider fits astride over radially outside and inside rims of the track rail to conform the track rail, and the return passages are made opened on the forward and aft end faces at locations that are above the outside and inside rims of the track rail and closer to the centroidal axis of the track rail than the outside and inside rims of the track rail. Moreover, the slider has widthwise opposing side surfaces extending lengthwise of the slider in parallel with each other.
With the curvilinear motion guide unit constructed as stated earlier, the casing of the slider has the forward and aft end faces included in planes extending through the center of curvature of the track rail and normal to the top surface of the track rail. That is to say, even when the casing is modified in length along the track rail depending on the variations in specifications of the curvature of the track rail and corresponding changes in overall length of the slider, the forward and aft end faces of the casing always remain residing in planes extending through the center of curvature of the track rail and normal to the top surface of the track rail. This makes the end caps interchangeable, allowing the end caps with the turnarounds to be common in specification to a variety of the track rails modified in curvature. Moreover, the return passages are arranged closer to the centroidal axis of the track rail than the radially outside and inside sides of the track rail. Thus, the casing has not to arrange the return passages widthwise outwardly beyond the radially outside and inside sides of the track rail. As a result, since the return passages may be made opened at the same locations on the end faces regardless of the variations in curvature of the track rail, the end caps can be made interchangeable to the units modified in specification. In addition, the casing may be made reduced widthwise in size with well balance.
In accordance with another aspect of the present invention, a curvilinear motion guide unit is disclosed, wherein the end caps are each provided therein with a claw to scoop the rolling elements out of the associated raceway, while the first raceway grooves on the track rail are each made with a channel in which a claw fits for movement. The claws formed in the end caps travel in the channels at the bottoms of the first raceway grooves during curvilinear movement of the slider to scoop the rolling elements out of the raceway grooves and transfer them to the turnarounds in the end caps, helping ensure the smooth recirculation of the rolling elements. Then, the claws lead gently the rolling elements out of the turnarounds into the raceways, allowing the rolling elements to land softly in the raceways.
In accordance with a further another aspect of the present invention, a curvilinear motion guide unit is disclosed, wherein both a top surface and any one of the side surfaces of the casing include planar reference surfaces for mounting to locate with precision other member that is to be mounted to the casing. Moreover, the casing includes mounting surfaces on which the other member is fixed, the mounting surfaces being drilled with threaded holes. Thus, positioning of the casing to the other member will be simply made with accuracy, and further, fixing the other member to the mounting surface may be also made easily by only driving the bolts into the threaded holes with the other member being kept in place.
In accordance with another aspect of the present invention, a curvilinear motion guide unit is disclosed, wherein the return passages made in the casing are linear bores that run straight through the casing from any one of the forward and aft end faces to the other. Thus, the return passages extend in parallel with the direction of the tangent, or the chord, at a sliding point on the track rail along which the slider moves. Such linear passages may be simply bored by the use of any conventional boring machines. Rolling elements led into the return passages from the turnarounds in any one of the end caps are allowed to run by the shortest route to the other turnarounds.
In accordance with another aspect of the present invention, a curvilinear motion guide unit is disclosed, wherein the casing is made with admission holes through which a desired number of the rolling elements may be charged into the recirculating passages, and the admission holes are communicated to the return passages and may be closed with plugs. According to the construction described just above, the desired number of the rolling elements are first fed into the return passages and then reach the raceways through the turnarounds. The plugs to close the admission holes are to keep the charged rolling elements from going back out of the admission holes. Moreover, the plugs serve to prevent foreign matter such as dust and dirt from entering into the recirculating passages, and to keep lubricant such as grease from leakage.
In accordance with another aspect of the present invention, a curvilinear motion guide unit is disclosed, wherein the end cap is cut deep to form a slit open to the side facing the track rail so that the end cap, when fitting astride over the track rail, may be stretched apart at the slit to be easily placed over the track rail.
In accordance with another aspect of the present invention, a curvilinear motion guide unit is disclosed, wherein the end seal is composed of a rubber plate and a metal backing plate bonded to the rubber plate, the metal backing plate being comprised of a pair of backing halves to be stretched apart from each other when the end seal is placed astride over the track rail. With the end seal constructed as described earlier, the rubber plate may flex at the middle area to place easily the end seal over the track rail.
In accordance with a further another aspect of the present invention, a curvilinear motion guide unit is disclosed, wherein the track rail is formed in a loop, over which the sliders ride astride for curvilinear movement. With the curvilinear motion guide unit constructed as stated just above, the guide unit may be used between the members, for example base and turntable, rotating relative to one another with the base being fixed to the track rail while the turntable being mounted to the slider. An unitary member might be mounted to all of the sliders or, in contrast, many members might be mounted some sliders.
Other objects and features of the present invention will be more apparent to those skilled in the art on consideration of the accompanying drawings and following specification wherein are disclosed preferred embodiments of the invention with the understanding that such variations, modifications and elimination of parts may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.